Resistor unit



Sept. 13, 1932. G, E, MEGOW 1,877,352

RBSISTOR UNIT Filed MaICh 11, 1929 319.9' @SWOQMWY Patented Sept. 13, i932 UNITED STATES PATENT OFFICE GEORGE E. MEGOW, OF vSOUTH MILWAUKEE, WISCONSIN, ASSIGNOR, BY MESNE AS- SIGNMENTS, TO ALLEN-BRADLEY COMPANY, OF MILWAUKEE, WISCONSIN, A COR- PORATION oF wIscoNsIN BESISTOR UNIT Application led Harch.11,v1929. Serial No. 346,086.

This invention relates to certain new and useful improvements in molded resistor units andthe method of forming the same, and has as one of its objects to provide greater mechanical strength for such units.

Another object of this invention resides in the provision of a resistor unit of the character described, so constructed that its over-all length may be comparatively reduced without lowering its resistance value.

A further object of this invention resides in the provision of a resistor unit of the character described in which substantially 90% of the over-all length ofthe unit serves as active resistance material.

And a still further object of this invention resides in the method of forming ay resistor unit of the character described wherein the usual paper protecting tube extends into the end cap members to increase the mechanical strength of the unit and to insulate the same therefrom except at its very'ends.

lVith the above and other objects in View, which will appear as the description proceeds, my invention resides thenovel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

In the accompanying drawing, I have illustrated one complete example of the physical embodiment of my invention constructed according to the best mode I have so far devised for the practical application of the principles thereof, and in which:

Figure 1 is an elevational view of a completed resistor unit embodying my invention;

Figures 2, 3, 4 and 5 illustrate the unit at various stages of completion;

Figure 6 1s a View of the unit with one cap member in position and showing the other removed therefrom;

Figure 7 is a cross sectional view taken through Figure 6 on the plane of the line 7-7; and

Figure 8 is a view similar to Figure 1 illustrating an extremely small, or midget, resistor element, the construction of which this invention is particularly adapted for.

Referring now more particularly to the accompanying drawing, in which like numerals designate like parts, the numeral 5 designates generally a resistor unit formed in accordance with my invent-ion and to the ends of which caps or terminal members 6 are secured to facilitate its connection in a circuit, by being held between conventional mounting clips, or by having suitable conductors soldered to the caps.

The unit 5 comprises a rod or stick of resistance material 7 molded in the usual manner, from materials having the desired conductive characteristics. After the stick 7 has been formed, its ends are dipped into, or otherwise coated, with a conducting cement depicted at 8, in Figure 2. The unit with its ends thus coated is then baked at approximately 325 degrees F., allowed to cool, and calibrated, the coating of conducting cement providing a perfect contact during the calibration of the unit to insure accuracy.

Following the Calibrating process, the unit is enclosed in a paper, or other like insulating material, tube 9, the length of which is slightly less than the over-all length of the unit 7, so that its ends project. beyond the paper tube approximately 12 ot an inch as illustrated in Figure 3. The ends of the enclosed unit are then again dipped into, or otherwise coated with the conducting cement, as at 10, in Figure 4, and baked at approximately 250 degrees F. During this second baking, the conducting cement cracks slightly due to the drying out of the paper tube, but it is desirable and, in fact, necessary that this cracking or drying out of the aper tube takes place before the final assemiily of the unit.

Vit-h thegunit thus heat cured or dried, it has its ends dipped or coated for a third time to place a. heavy coating 11 thereon which. is air dried to a substantially plastic state. The caps or terminal members 6 are then pressed onto the coated ends 1,1, as illustrated in Figure 6. l

The inner diameter of the caps 6 at their open ends is substantially the samey as the isv outer diameter of the paper tube 9, being slight-ly taperingly reduced towards their inner closed ends so that as they are pressed onto the unit all excess conducting cement ll is forced out ot the. caps through openings G in their closed ends. The slight taper ol' the walls of the cap wedges the ends of the paper tube between the resistor unitl ends and the inner walls of the caps and provides a substantially resilient seat for the caps and protects the ends ot the resistor units. 'l`be extension ot' the paper tube 9 into the caps- G greatly increases the nieelmnical strength of the unit and is tar more desirable than it the cap is directly pressed onto the resistance unit because the material thereof develops fractures when subjected to severe strains.

To prevent crunching ot the clubI ot' tbe paper tube 9, the mouths ot the caps are slightly flared, as at 12.

The extension of the paper tube ends into the. caps (i not only increases the mechanical strength ot' the unit but also makes possible the use of a greater portion of the over-all length otl the unit Jfor active resistance material as it provides an electrical. connection between the unit and the, end cap members only at the very ends ot the unit. In this manner, it is possible to economically manufacture resistor units considerably smaller than has heretofore been possible. A resistor of thisI Character is illustrated in Figure 8. in which the tapered end caps (5 are replaced by caps 13 having flat ends. lVith this cmistruction substantially QUI/l, of the. over-all length of the unit serves as active resistance material.

As the end caps G are apt to become loosened during use and may possibly pull away from the ends of the resistor, means are provided which insures continuity of contact between the. caps and the ends of the units. This consists in forming channels or grooves` 14 in the walls ot the end caps tl and 13 which are filled with conducting cement as the caps are pressed into position so that even though a cap pulls slightly away trom the unit, the continuity" is maintained by the ribs of conducting cement which till the grooves 14 and connect with the cement adhering to the ends of the, unit.

The conducting cement used. consists preferably of approximately 50S/U phenol condensat-ion product and 50% graphite mixed with denatured alcohol to a working consistency.

From the foregoing description, taken in connection with the accompanying drawing, it will be readily apparent to those skilled in the art to which an invention of the character described appertains, that l provide. a resister unit and a method of forming the. same in which the mechanical strength of the unit is greatly increased and in which aV greater percentage ot' the over-all length of the unit is available as active resistance material.

Vhat I claim as my invention is:

1. A resistor unit of the character described comprising a molded body member, a non-conducting member enclosing the body member to within substantially the end thereof., an end cap engaged over the end of the body member and snugly engaging the non-conducting member to compress` the same between the inner wall of the end cap and the body member and trictionally retain the end cap on the body member, conducting material filling the space within the end cap not consumed by the body member to electrically connect the end cap with the body member extreme end, and a rib of conducting material extended inwardly from the conducting material lilling the space within the end cap and over the. exterior of the non-conductingr member within a groove in the end cap for maintaining the electrical connection between the. end cap and the bod member in the event the end cap moves slig tly away from the end of the body melliber.

2. In a resistor unit of the character described, a body member, an insulating member enclosing the body member to substantially the end thereof, an end cap engaged over the end ot the body member and the insulating member, conducting material disposed between the end cap and the body member and to provide an electrical connection therebetween, and ribs of conducting material extended inwardly from the conducting material between the, end cap and the body member and overlying the insulating member for insuring electrical connection between the end cap and the body member in the event the end cap moves slightly away from the end of the body member, said ribs of conducting material being received in grooves formed in the end cap.

3. In a resistor unit of the character described, a body member, an insulating member wrapped about the body` member and leaving its extreme end exposed, an end cap mounted on the end of the body member and projected over the insulating wrapper with its ma'or portion in intimate engagement with tie wrapper, and conducting cement providing electrical connection between the end of the body member and the end cap, said end cap being provided with longitudinal grooves which are filled by the conducting cement to insure electrical connection between the end cap and the end of the resistor body member in the event the end cap pulls away from the end of the body member.

4. The hereindescribed method of forming resistor units which consists in en asing the unit in insulating material to a, point spaced slightly from its ends, in dipping the ends of the encased unit in conducting cement,

and in pressing cap members onto the ends of i the encased unit whereby contact is made between the cap members and the resistor unit only at its very ends.

5. The hereindescribed method of form- 5 ing a resistor unit which consists in positioning a paper tube over a molded unit with its ends terminating directly adjacent the ends of the unit, in applying a conducting material to thel ends of the unit, in baking the '10 unit with the conducting material over the ends thereof to remove the moisture content of the paper tube, in again applying a conducting material to the ends of the unit to provide a relatively heavy coating of said conducting material on the ends thereof, and in forcing metallic terminal members onto ends of the unit while the conducting material is in a sub-plastie state to insure a positive electrical connection between the terminal members and the extreme ends of the molded unit.

In testimony whereof I have hereunto affixed my signature.

GEORGE E. MEGOW. 

